The present invention relates to diaphragm valve of the kind suitable for use particularly, but not exclusively, in semiconductor manufacturing equipment.
Diaphragm valves of the kind described are disclosed in JP 6-341560A, 6-193747A and 6-94142A.
FIG. 3 of the accompanying drawings is a longitudinal, sectional view showing the essential part of a diaphragm valve according to JP 6-341560A. In FIG. 3, the diaphragm valve comprises a body A defining a valve chamber B and first and second passageways through the body which, in use, serve as an inlet and an outlet for the valve chamber. The valve chamber B accommodates a flexibly resilient diaphragm C, a valve seat D and a seat holder E. The diaphragm and seat holder are held in place by means of a bonnet G, and the diaphragm is shaped such that when fitted in the valve chamber it is spaced from the valve seat D to allow fluid to flow in use between the two passageways. The bonnet G supports drive means F which are selectively operable for pressing against the diaphragm C for deforming the diaphragm and pushing it into contact with the valve seat D in order to close the valve. The valve seat D and seat holder E form an integral unit which is received in the valve chamber B.
An advantage of the diaphragm valve shown in FIG. 3 is that when the drive means are operated to press the diaphragm C against the valve seat D, the valve seat D is hardly deformed. However, a disadvantage of the diaphragm valve of JP 6-341560A is that if the valve seat D becomes damaged, then both seat D and holder E need to be replaced which may be expensive.
FIG. 4 is a longitudinal, sectional view showing the essential part of a diaphragm valve in accordance with JP 6-94142A. In the diaphragm valve of FIG. 4, the valve seat D and seat holder E are separate components which are installed separately into the valve chamber B. Thus, if seat D becomes damaged, then it is necessary only to replace seat D, leading to lower repair costs as compared with the valve of FIG. 3.
However, a disadvantage of the diaphragm valve of FIG. 4 is that when the diaphragm C is pushed against the seat D, the seat is sometimes deformed allowing fluid to leak between the body A and seat D.
As described above, the arrangements of valve seats and seat holders in the prior art diaphragm valves have both advantages and disadvantages. Accordingly, it is an object of the present invention to provide improvements in or relating to diaphragm valves of the kind described.
In particular, it is an object of the present invention to provide an improved diaphragm valve which has minimal associated repair costs and, at the same time, has no risk of leaking.
A particular object of the present invention is to provide an improved diaphragm valve in which the valve seat does not deform when pressed by the diaphragm.
According to the present invention therefore there is provided a diaphragm valve assembly comprising a body defining a valve chamber and first and second passageways through the body which, in use, serve as an inlet and outlet for the valve chamber; a removable valve seat adapted to be installed in the valve chamber around one of said passageways, seat holding means for holding the valve seat in place in the valve chamber, said seat holding means comprising a seat holder that is shaped to surround said valve seat, a flexibly resilient diaphragm having a valve closing portion and means for holding the diaphragm in position in the valve chamber, such that the valve closing portion is disposed juxtaposed the valve seat, the diaphragm being shaped that when fitted its valve closing portion is spaced from the valve seat, and selectively operable driving means for driving the valve closing portion of the diaphragm into contact with the valve seat for closing the valve; characterised in that said body includes a protruding rim portion around said one passageway, the arrangement being such that said rim portion and said seat holder define a recess adapted to receive the valve seat such that the valve seat is held between the seat holder and the rim portion.
In operation, the driving means may be operated to drive the valve closing portion of the diaphragm against the valve seat to prevent fluid flow between the two passageways. If the pressure applied to the diaphragm by the driving means is removed, then the diaphragm is allowed to return resiliently to its original shape and position such that the valve closing portion of the diaphragm moves away from the valve seat. The passageways through the body can then communicate with one another to allow fluid flow from the one passageway to the other passageway.
Advantageously, the valve seat is a separate component, independent of the body and seat holder. Thus, if the seat become damaged, then the seat alone needs replacement. It will be appreciated that this minimises the costs associated with repairing the valve.
Furthermore, the valve seat, when fitted, is held between the seat holder and rim portion which reduces the risk of deformation of the seat to nil when the diaphragm is pressed against the valve seat, thereby producing no risk of leakage between the valve seat and the body. Said valve seat is preferably annular and said rim portion is preferably cylindrical. The seat holder and rim portion preferably define an annular recess therebetween for receiving said annular valve seat. Said rim portion may have a shaped, preferably cylindrical, outer surface, and said valve seat may have a correspondingly shaped, preferably substantially cylindrical, inner surface adapted to contact the outer surface of the rim portion. The valve seat may have shaped outer surface, and the seat holder may have a correspondingly shaped inner surface adapted to contact the outer surface of the valve seat. Preferably, the valve seat forms a snug or tight fit in the annular recess defined by the rim portion and seat holder such that the valve seat is held firmly in the recess and is reinforced against deformation when the diaphragm valve is urged against the seat. In some embodiments, the valve seat may be xe2x80x9cpinchedxe2x80x9d between the rim portion and seat holder.
Said body may define a floor surface within the valve chamber, which floor surface comprises annular seat supporting surface around the rim portion, which annular seat supporting surface is adapted to contact and support the valve seat. Said floor surface may be rebated around the seat supporting surface to form a seat bolder channel adapted to receive the seat holder Thus, the seat holder channel or groove is preferably formed deeper into the body of the diaphragm valve than the seat supporting surface of seat base. This allows the valve seat and di seat holder to be properly positioned and the valve seat to be securely held by the seat holder and the protruding rim. The seat holder may also be annular and accordingly the seat bolder channel maybe annular.
Normally, the one passageway is adapted to form the inlet in use, with the other passageway forming the outlet. The one passageway may be formed substantially centrally within the body, and the protruding rim, seat supporting surface and seat holding channel may be formed substantially concentrically with the one passageway.
Following is a description by way of example only, with reference to the accompanying drawings of embodiments of the present invention.